Conversion of hydrocarbons



Reissued May 28, 1940 21.461 convsnsrou or nrnaocaanons Jacquie o.Morrell and Arlstid v. Grosse, Chicago,

Ill., assignors to Universal Oil Products Company, Chicago, 111., acorporation Delaware No Drawing. Original No. 2,124,586, dated July 26,1938, Serial No. 105,715, October 15, 1986. Application for reissueSeptember 15, 1939,

Serial No. 295,11l.

8 Claims. (01. 260-668)- This invention relates particularly to theconversion of straight chain hydrocarbons into closed chain or cyclichydrocarbons.

More specifically, it is concerned with a process involving the use ofspecial catalysts and specific conditions of operation in regard totemperature, pressure and time of reaction whereby aliphatichydrocarbons can be efllciently converted into aromatic hydrocarbons.

In the straight pyrolysis of pure. hydrocarbons or hydrocarbon mixturessuch as those encountered in fractions from petroleum or other naturallyoccurring or synthetically produced hydrocarbon mixtures the reactionsinvolved which produce aromatics from paraflins and oleflns are of anexceedingly complicated character and cannot be very readily controlled.

It is generally recognized that, in the thermal decomposition ofhydrocarbon compounds or hydrocarbon mixtures of relatively narrow rangethat whatever intermediate reactions are involved, there is an overallloss of hydrogen, a tendency to carbon separation and a generally widerboiling range in the total liquid products as compared with the originalcharge. Under mild cracking conditions involving relatively lowtemperatures and pressures and short times of exposure to crackingconditions it is possible to some extent to control cracking reactionsso that they are limited to primary decompositions and there is aminimum loss of hydrogen and a maximum production of low boilingfractions consisting of compounds representing the fragments of theoriginal high molecular weight compounds.

As the conditions of pyrolysis are increased in severity using highertemperatures and higher t mes of exposure to pyrolytic conditions, thereis a progressive increase in loss of hydrogen and a large amount of"secondary reactions involving recombination of primary radicals to formpolymers and some cyclization to form naphthenes and aromatics, but themechanisms involved in these cases are of so complicated a nature thatvery little positive information has been evolved in spite of the largeamount of experimentation which has been done and the large numberoftheories proposed. In general, however, itmay.

be said that, starting with paraflin hydrocarbons representing thehighest degree of saturation, these compounds are changed progressivelyinto olefins, naphthenes, aromatics, and finally into carbon andhydrogen and other light fixed gases.

It is not intended to infer from this statement basic laws or rules forpredicting the effectiveness of catalytic materials and the art as awhole is in a more or less empirical state. In using catalysts even inconnection with conversion reactions among pure hydrocarbons andparticularly in connection with the conversion of the relatively heavydistilla'tes and residua which are available for cracking, there is ageneral tendency for the decomposition reactions to proceed at a veryrapid rate, necessitating the use of extremely short time factors andvery accurate control 01' temperature and pressure to avoid tooextensive decomposition. There are further difficulties encountered inmaintaining the sillciency at catalysts employed in pyrolysis sincethere is usually a rapid deposition of carbonaceous materials on theirsurfaces and in their pores.

The foregoing brief review of the art of hydrocarbon pyrolysis is givento furnish a. general background for indicating the improvement in suchprocesses which is embodied in the present invention, which may beapplied to the treatment of pure parafiin or olefin hydrocarbons,bydrocarbon mixtures containing substantial percentages of parafilnhydrocarbons such as relatively close out fractions producible bydistilling petroleum, and analogous fractions which con tain unsaturatedas wellas saturated straight chain hydrocarbons, such fractionsresulting from cracking operations upon the heavier fractions ofpetroleum.

In one specific embodiment, the present invention comprises theconversion of aliphatic hydrocarbons including paraflln and olefinhydrocarbons into aromatic hydrocarbons by subjecting them at elevatedtemperatures of the order of 400-700 C.,to contact for definite times ofthe order of 6-50 seconds with catalytic materials comprising majorproportions of aluminum oxide of relatively low catalytic activitysupporting minor proportions of oxides of elements selected from thoseoccurring in the left hand columns of group V of the periodic table,these oxides having relatively high' catalytic activity.

According to the present invention aliphatic or,

straight chain hydrocarbons having 6 or more carbon atoms in chainarrangement in their structure are specifically dehydrogenated in such away that the chain of carbon atoms undergoes ring closure with theproduction in the simplest case of benzene from n-hexane or n-hexene andin the case of higher molecular weight paramns of various alkylderivatives of benzene. Under properly controlled conditions of times ofcontact, temperature and pressure, very high yields of the order of 75to 90% of the benzene or aromatic compounds are obtainable which are farin excess of any previously obtained in the-art either with or withoutcatalysts. For the sake of illustrating and exemplifying the types ofhydrocarbon conversion reactions which are specifically acceleratedunder the preferred conditions by the present types of catalysts, thefollowing structural equations are introduced.

In the foregoing table the structural formulas of the primary parafiinhydrocarbons have been represented as a nearly closed ring instead of bythe usual linear arrangement for the sake of indicating the possiblemechanisms involved. No

attempt has been made to indicate the possible intermediate existence ofmono-oleflns, diolefins. hexamethylenes or alkylated hexamethyleneswhich might result from the loss of various amounts of hydrogen. It isnot known at the present time whether ring closure occurs at the loss ofone hydrogen molecule or whether dehydrogenation of the chain carbonsoccurs so that the first ring compound formed is an arcmatic such asbenzene or one of its derivatives The above three equations are of arelatively simple character indicating generally the type of reactionsinvolved but in the case of n-paraffins or mono-olefins of highermolecular weight thantheoctaneshownandinthecaseof branch chain compoundswhich contain various alkyl substituent groups in different positionsalong the six-carbon atom chain, more complicated reactions will beinvolved. For example in the case 'of such a primary compound as2,8-dimethyl hexone the principal resultant product is apparently-o-xylene although there are concurrently produced definite yields ofsuch compounds as ethyl indicating an isomeriaation of twosubtmethylgroups. Inthecaseofnonanes which are represented by thecompound 2.8,

wtrimethylhexanmthereisformationnotonlyof mesitylene but also of suchcompounds as methyl ethylbsnaolandvariouspropylbensols.

It will be seen from the foregoing that the scope of the presentinvention is preferably limited to the treatment of aliphatichydrocarbons which contain at least 6 carbon atoms in straight chainarrangement. In the case of parafiin hydrocarbons containing less than 6carbon atoms in linear arrangement, some formation of aromatics may takeplace due to primary isomerization reactions although obviously theextent of.

these will vary considerably with the type of compound and theconditions ofopera'tion. The

process is readily applicable to paraflins from hexane up to do-decaneand their corresponding olefins. With increase in molecular weightbeyond this point the percentage of undesirable side reactions tends toincrease and yields of the desired alkylated aromatics decrease inproportion.

According to the present invention composite catalytic materials areemployed which comprise in general major proportions by weight ofgranular activated aluminum oxide as a base catalyst of supportimaterial for minor proportions of oxides of the elements in the lefthandcolumn of group V of the periodic table comprising the elementsvanadium, columbium and tantalum. The base material comprising aluminumoxide is of relatively low catalytic activity while the oxides of theelements mentioned are of relatively high catalytic activity and furnishby far the greater proportion of the observed catalytic effects. Theoxides of these several elements vary somewhat in catalytic activity inany given reaction comprised wlthin the scope of the invention and thisvariation may further vary in the case of different types ofdehydrogenation and cyclization reactions. Some of the properties ofthese catalytically active oxides, which are developed on the surfaceand in the pores of the alumina particles will be described insucceeding paragraphs.

It should be emphasized that in the field of catalysis there have beenvery few rules evolved .which will enable the prediction of whatmaterials will catalyze a given reaction. Most of the catalytic. workhas been done on a purely empirical basis, even though at times certaingroups of elements or compounds have been found to be more or lessequivalent in accelerating certain types of reactions.

Aluminum oxide which is preferred as base material for the manufactureof catalysts for the process may be obtained from natural aluminum oxideminerals or ores such as bauxite or carbonates such as dawsonite byproper calcinatlon, or it may be prepared by precipitation of aluminumhydroxide from solutions of aluminum sulfate or different slums, anddehydration of the precipitate of aluminum hydroxide by heat. Usually itis desirable and advantageous to further treat it with air or othergases, or by other means to activate it prior to use.

Two hydrated oxides of aluminum occur in nature, to-wit: bauxite havingthe formula AlaO:.2H:O and diaspore AlzOsHzO. In both of these oxidesiron sesqui-oxide may partially replace the alumlna. These two mineralor corresponding oxides produced from. precipitated and aluminumhydroxide are particularly suitable for the manufacture of thepresent'type of catalystsandinsomeinstanceshavegiventhebestresultsofanyofthebasecompoundswhoseuseisat present contemplated. The mineral dawsonite having the formulaNasAl(CO:):.2Al(OH)= is anothermineralwhichmavbeusedasasource ofaluminum It is best practice in the mal steps-of preparing aluminumoxide as a base catalyst to'ignite it for some time at temperatureswithin the approximate range of from BOO-900 C. This probably does notcorrespond to complete dehydration of the hydroxides but apparentlygives a catalytic material of good strength and porosity so that it isable to resist for a long period of time the deteriorating effects ofthe service and regeneration periods to which it is subjected.

Our investigations have also definitely demonstrated that the catalyticefiiciency of alumina. which may have some catalytic potency in itselfis greatly improved by the presence of oxides of the preferred elementsin relatively minor amounts, usually of the order of less than 10% byweight of the carrier. It is most common practice to utilize catalystscomprising 2 to 5% by weight of these oxides, particularly the loweroxides.

The oxides which constitute the principal active catalytic materials maybe deposited upon the surface and in the pores of the activated aluminagranules by several alternate methods such as for example, the ignitionof nitrates which have been adsorbed or deposited from aqueous solutionby evaporation or by a similar ignition of precipitated hydroxides. Asan alternative method though obviously less preferable, the finelydivided oxides may be mixed mechanically with the alumina granuleseither in the wet or the dry condition. The point of achieving the mostuniform practical distribution of the oxides on the alumina shouldconstantly be borne in mind since the observed catalyticeffectsevidently depend principally upon a surface action.

The oxide of vanadium which results from the ignition of the nitrate,the hydroxide or the carbonate is principally the pentoxide V205 whichis reduced by hydrogen at a red heat to form the tetroxide V204 or thecorresponding dioxide V0: and then to the sesquioxide V203. In any casethe primary deposition of vanadium compounds upon alumina granules maybe made by the use of the soluble vanadyl sulfate or the nitrate andalso solutions of ammonium and alkali metal vanadates may be employed,which furnish alkaline residues on ignition. It is probable that thesesquioxide is the principal compound which accounts for the catalyticactivity observed with vanadium catalysts in reactions of the presentcharacter.

operation so that the essential catalysts for the major proportion of arun will probably include the lower oxides CbOz, CbzOa and CbO.

The element tantalum which is the lowestmember of the present group ofelements in the periodic table has the pentoxide T8205, 8 tetroxideT3204 and probably a sesquioxide TazOa. The

higher oxide is prepared by the ignition of the precipitatedpentahydroxide precipitated from soluble salts.

- the best results in any given instance.

It has been found essential to the production of high yields ofaromatics from aliphatic hydrocarbons when using the preferred types ofcatalysts that depending upon the aliphatic hydrocarbon or mixture ofhydrocarbons being treated, temperatures from 400-700 C. should beemployed, contact times of approximately 6 to 50 seconds and pressureapproximating atmospheric. The use of sub-atmospheric pressures of theorder of atmosphere may be beneficial in that reduced pressuresgenerally favor selective dehydrogenation reactions but; on the otherhand moderately superatmospheric pressure usually of the order of lessthan pounds per square inch tend to increase the capacity of commercialplant equipment so that in practice a balance is struck between thesetwo factors. The times of contact most commonly employed withn-paraillnic or mono-olefinic hydrocarbons having from 6-12 carbon atomsto the molecule are of the order of 6-20 seconds. It will be appreciatedby those familiar with the art of hydrocarbon conversion in the presenceof catalysts that the factors of temperature, pressure and time willfrequently have to be adjusted from the results of preliminaryexperiments to produce The criterion of the yield of aromatics willserve to fix the best conditions of operation. In a general sense therelations between time, temperature and pressure are preferably adjustedso that rather intensive conditions are emplbyed of sumcient severity toinsure a maximum amount of the desired cyclization reactions with aminimum of undesirable side reactions. If too short times of. contactsare employed the'conversion reactions will not proceed beyond those ofsimple dehydrogenation and the yields of olefins and diolefins willpredominate over those of aromatics.

While the present process is particularly applicable to the productionof the corresponding aromatics from an aliphatic hydrocarbon or amixture of aliphatic hydrocarbons, the invention may also be employed toproduce aromatics from v aliphatic hydrocarbon mixtures such asdistillates' .covered as such by distillation in fractions of properboiling range followed by chemical treatment with reagents capable ofreacting selectively with them. Another method of aromatic concentrationwill involve the use of selective solvents such as liquid sulfurdioxide, alcohols, furfural, chlorex, etc.

In operating the process the general procedure is to vaporizehydrocarbons or mixtures of hydrocarbons and after heating the vapors toa suitable temperature within the ranges previously specified, to passthem through stationary masses of granular catalytic material invertical cylindrical treating columns or banks of catalyst-containingtubes in parallel connection. Since the reactions are endothermic it maybe necessary to apply some heat externally to maintain thc best reactiontemperature. After passing through the catalytic zone the products aresubmitted to fractionation to recover cuts or fractions containing thedesired aromatic product with the separation of fixed gases, unconvertedhydrocarbons and heavier residual materials, which may be disposed of inany suitable manner depending upon their If desired and foundcomposition. The overall yield of aromatics may be increased byrecycling the unconverted straight chain hydrocarbons to furthertreatment with fresh material, although this is a more or less obviousexpedient and not specifically characteristic'of the present invention.

.It is an important feature of the present process that the vaporsundergoing dehydrogenation should be free from all but traces of watervapor since the presence of any substantial amounts of steam reduces thecatalytic selectivity of the composite catalyst to a marked degree. theempirical state of the catalytic art, it is not intended to submit acomplete explanation of the reasons for the deleterious influence ofwater vapor on the course of the present type of catalyzed reactions,but it may be suggested that the action of the steam may be to cause apartial hydration of alumina and some of the catalytic oxides due topreferential adsorption so that in effect the hydrocarbons are preventedfrom reaching or be- 1 ing adsorbed by the catalytically active surface.

The present types of catalysts are particularly effective in removinghydrogen from chain compounds in such away that cyclization may beprompted without removal of hydrogen from end oxidizing gas at amoderately elevated temperature, usually within the range employed inthe dehydrogenation and cyclization reactions. This oxidationeffectively removes traces of carbon deposits which contaminate thesurface of the particles and decrease their efliciency. It, ischaracteristic of the present types of catalysts that they may berepeatedly regenerated with only a very gradual loss of catalyticemciency.

During oxidation with air or other oxidizin gas mixture in regeneratingpartly spent material, there is evidence to indicate that the loweroxides are to a large extent, if not completely, oxidized to higheroxides which combine with aluminum oxide to form aluminum salts ofvariable composition. Later these salts are decomposed by contact withreducing gases in the first stages of service to reform the lower oxidesand regenerate the real catalyst and hence the catalytic activity.

Example I The charging stool: employed was a n-hexane fraction obtainedfrom a highly paraflinic crude petroleum by a close fractionationthereof. This material was vaporized and passed over a granular catalystcomprising vanadium sesquioxide supported on an alumina The catalystwasprepared by utilizing a substantially saturated solution of ammoniummetavanadate which was added to about its weight of aluminum oxide intwo successive portionstc avoid excessive wetting of the particles, thesolvent being evaporated after the addition of the first half of thesolution. a careful ignition during which period ammonia and water wereevolved left a residue of vanadium pentoxide which was reduced by astream of hydrogen at In view of about 250 C., for several hours toproduce the lower oxide.

The yield of benzol from a once-through operation at a temperature of505 C., atmospheric pressure and about 18 seconds contact time was about48% by weight of the hexane fraction charged. This yield was finallyraised to approximately 75% by recycling.

Example I! A catalystwas prepared by utilizing a mixed double fluorideof potassium and columbium in solution and precipitated columbiumpentahydroxide on the particles after which the dioxide Cb'Oz wasobtained by controlled ignition of the catalyst particles.

A reduction by hydrogen at a red heat for 2-3 hours preceded the use ofthe catalyst.

n-Heptane was vaporized and subjected to contact with the catalyst at atemperature of 560 C., atmospheric pressure, and 12 seconds contact timeto produce a 56% yield of toluene on a once-through basis and a finalyield of 76% of a recycle basis.

Example III As a further example of the applicability of the presenttypes of catalysts'and the preferred conditions of operation forproducing aromatics from oleflns, an example involving the conversion ofn-heptene to toluene may be cited. The catalyst employed was columbiumoxides on alumina and was prepared in general accordance with theprocedure outlined in Example 11. At a temperature of 505 C.,substantially atmospheric pressure and a time of contact of about 18seconds, there was produced a yield of toluene equal in weight to about74% of the n-heptene charged. Recycling again increased the overallyield to 90%.

- Erampl'e- IV A catalyst was made by suspending activated aluminaparticles in a solution of tantalum potassium fluoride and precipitatingwith caustic soda to form the tantalum pentahydroxide. The

phatic hydrocarbons, although neither section is intended to be undulylimiting.

We claim as our invention:

1. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cycliclzing the allphatic hydrocarbon by subjectionto a temperature of the order of 400 to 700 C., for a period of about 6to 50 seconds, in the presence of an aluminum oxide catalyst containinga relatively small amount of an oxide. of a metal from the left handcolumn of group V of the periodic table and selected from the classconsisting of vanadium, columbium and tantalum.

2. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of 1 aluminum oxide catalyst containing a relatively smallamount of an oxide of vanadium.

3. A process for the production of aromatic 'hydrocarbons from aliphatichydrocarbons. of

from six to twelve carbon atoms, which comprises dehydrogenating andcyclicizing the aliphatic hydrocarbon by subjection to a temperature 01'the order of 400 to 100 C., for a period of about 6 to 50 seconds, inthe presence of an aluminum oxide catalyst containing a relatively smallamount of an oxide of columbium.

4. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the allphatic hydrocarbon by subjectionto a temperature of the order of 400 to 700 C., for a period of about 6to 50 seconds, in the presence of an aluminum oxide catalyst containinga relatively small amount of an oxide or tantalum.

5. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the aliphatic hydrocarbon by subjectionto a temperature oi the order of 400' to 700 C., for a time period ofless than 50 secondsbut suflicient to dehydrogenate and cyclicize thealiphatic hydrocarbon, in the presence of an aluminum oxide catalystcontaining a relatively small amount of an oxide of a metal from theleit hand column 01' group V of the periodic table and selected from theclass consisting of vanadium, columbium, and tantalum.

6. Apro'cess tor' the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the allphatic hydrocarbon by subjection'to a temperature of the order to 400 to 700 0., for a timedehydrogenateand cyclicize the aliphatic hydrocarbon, in the presence ofan aluminum oxide catalyst containing a relatively small amount of anoxide of vanadium.

7. A processfor the production of aromatic hydrocarbons from aliphatichydrocarbons of I from six to twelve carbon atoms, which comhydrocarbonby subjection to a temperature of the order of 400 to 700 C., for a timeperiod of less than 50 seconds but sufllcie'nt to dehydrogenate andcyciicize the aliphatic hydrocarbon, in'the presence of an aluminumoxide catalyst period 01 less than 50 seconds but suiilcient to 7containing a relatively. small amount of an oxide of tantalum.

JACQUE C. MORRELL. ARIS'IID V. GROSSE.

